Intervertebral disc disease in dogs
Thoracolumbar intervertebral disc herniation (TL IVDH) is known to have a lifetime prevalence of ~20% in the Miniature Dachshund, and is fatal in 25% of cases. There is a perception that dogs which are more severely affected require decompressive surgery to recover ambulation, and a small amount of evidence to support this. The severe clinical signs are distressing to owners and further compounded by high financial costs of cross sectional imaging and surgery. It is however known that some dogs will recover without the need for surgery, and in 2017 I carried out an extensive data mining exercise which showed that recovery rates of dogs suffering from TL IVDH treated with medical therapy are similar to those following surgical management in all grades of severity except the most severely affected dogs (Freeman and Jeffery, JSAP 2017: 58, 199-204).
My PhD student is studying dogs rendered non-ambulatory following acute TL IVDH and treated medically rather than surgically; these dogs receive an MRI scan to confirm diagnosis, followed by a second scan after three months of medical management. It is known that in some cases both in human and canine disc herniation the herniated material is removed by natural processes (Argent et al 2019) and we aim to document the frequency with which this occurs, and whether there is a correlation with recovery of ambulation.
We aim to provide answers to a number of questions:
- Can dogs rendered non-ambulatory following acute compressive thoracolumbar intervertebral disc herniation (TL IVDH) recover ambulation without decompressive surgery?
- By what mechanism may herniated intervertebral disc material be removed by natural processes from the vertebral canal in dogs treated conservatively for TL IVDH?
- Is recovery of ambulation and/or speed of recovery associated with removal of extruded disc material from the vertebral canal?
Ultimately we aim to provide an answer to the key question: In dogs suffering acute severe TL IVDH, which cases genuinely require surgical treatment, and which may recover just as well with medical management
There are many other unanswered questions surrounding the role of calcification in the pathogenesis of intervertebral disc extrusion in dogs as well as humans.
Some of the key questions we have are:
- Why do certain specific discs tend to extrude commonly, whereas others rarely do?
- Why do some extrusions cause calamitous irreversible spinal cord injury, whereas others only lead to minimal self-limiting pain?
- Why should disc calcification lead to an increased risk of disc extrusion?
Additional work being carried out currently by my MPhil student with the assistance of Jonathan Powell’s biominerals laboratory and Professor Rachel Oliver from the Dept of Materials Science and Metallurgy is aimed at identifying the role of calcification in IVDH. Several studies have attempted to investigate the role of calcification in human disc herniation (Grant et al 2016, Shao et al 2016), and we have begun to look more closely into the mineral analysis of extruded and non-extruded disc material. Our early results indicate, as expected, a very high level of calcium and phosphorous in extruded disc material removed from the vertebral canal of clinical cases, and we have now been able to establish the nature of this calcified material in both extruded and non-extruded discs. We are now attempting to determine biomechanical features of this material on a nanoscale using atomic force microscopy.
We aim compare calcification in extruded and non-extruded disc material,as well as in non-degenerate discs, looking for reasons why some discs extrude and others do not, and why some extrusions are so catastrophic but others relatively benign.
Finally we are involved in a newly launched Kennel Club screening scheme for Dachshunds which provides guidelines for breeding based on the numbers of calcified discs identified by radiography. We are able to offer a CT scan alongside the radiographs, a much more sensitive modality for identification of disc calcification, with the aim of following these dogs and assessing their likelihood of suffering IVDH later in life.
In addition to this work, I am collaborating with the work of bioengineer George Malliaras and Christopher Proctor, who have designed an electrical stimulation device intended to deliver an oscillating electrical field to injured spinal cord. Our aim is to implant a series of such devices onto the surface of the injured spinal cord in a series of dogs suffering acute severe injury as a result of intervertebral disc disease.This type of stimulation has been shown in both dogs and humans to improve recovery in severe spinal cord injury, but currently no commercially available stimulator is in use. This technology has the potential to improve outcomes in both dogs and people suffering severe spinal cord injury.
